For my desktop, I don’t have Bluetooth built-in, would I be able to connect wirelessly with a dongle that has Bluetooth 5.0?

Please try the following solutions:

1. Try to buy a dongle with a Broadcom chip inside.
2. Try to update the dongle's drive to the latest version.
3. Try to move your dongle a little bit close to the keyboard.
4. Try to buy the dongle from a well-known brand as their dongles usually have better compatibility.
5. Buy the dongle from somewhere with an exchange policy, like Amazon, since you might need to exchange it.